How a ‘solar battery’ could bring electricity to rural areas – A ‘solar flow’ battery could “Harvest (energy) in the Daytime and Provide Electricity in the Evening

New solar flow battery with a 14.1 percent efficiency. Photo: David Tenenbaum, UW-Madison

Solar energy is becoming more and more popular as prices drop, yet a home powered by the Sun isn’t free from the grid because solar panels don’t store energy for later. Now, researchers have refined a device that can both harvest and store solar energy, and they hope it will one day bring electricity to rural and underdeveloped areas.

The problem of energy storage has led to many creative solutions, like giant batteries. For a paper published today in the journal Chem, scientists trying to improve the solar cells themselves developed an integrated battery that works in three different ways.

It can work like a normal solar cell by converting sunlight to electricity immediately, explains study author Song Jin, a chemist at the University of Wisconsin at Madison. It can store the solar energy, or it can simply be charged like a normal battery.

“IT COULD HARVEST IN THE DAYTIME, PROVIDE ELECTRICITY IN THE EVENING.”

It’s a combination of two existing technologies: solar cells that harvest light, and a so-called flow battery.

The most commonly used batteries, lithium-ion, store energy in solid materials, like various metals. Flow batteries, on the other hand, store energy in external liquid tanks.

What is A ‘Flow Battery’

This means they are very easy to scale for large projects. Scaling up all the components of a lithium-ion battery might throw off the engineering, but for flow batteries, “you just make the tank bigger,” says Timothy Cook, a University at Buffalo chemist and flow battery expert not involved in the study.

“You really simplify how to make the battery grow in capacity,” he adds. “We’re not making flow batteries to power a cell phone, we’re thinking about buildings or industrial sites.

Jin and his team were the first to combine the two features. They have been working on the battery for years, and have now reached 14.1 percent efficiency.

Jin calls this “round-trip efficiency” — as in, the efficiency from taking that energy, storing it, and discharging it. “We can probably get to 20 percent efficiency in the next few years, and I think 25 percent round-trip is not out of the question,” Jin says.

Apart from improving efficiency, Jin and his team want to develop a better design that can use cheaper materials.

The invention is still at proof-of-concept stage, but he thinks it could have a large impact in less-developed areas without power grids and proper infrastructure. “There, you could have a medium-scale device like this operate by itself,” he says. “It could harvest in the daytime, provide electricity in the evening.” In many areas, Jin adds, having electricity is a game changer, because it can help people be more connected or enable more clinics to be open and therefore improve health care.

And Cook notes that if the solar flow battery can be scaled, it can still be helpful in the US.

The United States might have plenty of power infrastructure, but with such a device, “you can disconnect and have personalized energy where you’re storing and using what you need locally,” he says. And that could help us be less dependent on forms of energy that harm the environment.

Long-lasting solar cells from and “unexpected gray area” … U of Wisconsin-Madison Make Surprising Discovery

UW-Madison engineers found a way to dramatically extend the lifespan of solar energy-harvesting devices, which use energy from sunlight to generate hydrogen from water. Credit: iStock

University of Wisconsin-Madison materials engineers have made a surprising discovery that could dramatically improve the lifetime of solar energy harvesting devices.

The findings allowed them to achieve the longest-ever lifetime for a key component of some types of photovoltaic cells called the photoelectrochemical electrode, which uses sunlight to split water into its constituent parts of hydrogen and oxygen.

In a paper published July 24, 2018, in the research journal Nano Letters, a team led by UW-Madison materials science and engineering Ph.D. student Yanhao Yu and his advisor, Professor Xudong Wang, described a strategy that extended the lifetime of a photochemical electrode to a whopping 500 hours—more than five times (5X) the typical 80-hour lifespan.

Usually, these types of electrodes are made of silicon, which splits water well, but is highly unstable and quickly degrades when it comes into contact with corrosive conditions. To protect these electrodes, engineers often thinly coat their surfaces.

It’s a tactic that only delays their eventual breakdown—sometimes after a few days and sometimes within hours.

“Performance varies widely and nobody really knows why. It’s a big question,” says Wang, a professor of materials science and engineering at UW-Madison.

Intriguingly, the researchers didn’t make any changes to the coating material. Rather, they boosted the electrode’s lifetime by applying an even thinner coating of titanium dioxide than usual.

In other words, less really was more!

Key to this exceptional performance was the team’s discovery about the atomic structure of titanium dioxide thin films, which the researchers create using a technique called atomic layer deposition.

Previously, researchers believed that the atoms in titanium dioxide thin films adopted one of two conformations—either scrambled and disordered in a state referred to as “amorphous,” or locked into a regularly repeating and predictable arrangement called the crystalline form.

Crucially, researchers were certain that all the atoms in a given thin film behaved the same way. Crystalline or amorphous. Black or white. No in-between.

What Wang colleagues found, however, is a gray area: They saw that small pockets of an in-between state persisted in the final coatings—the atomic structure in these areas was neither amorphous nor crystalline. These intermediates have never been observed before.

“This is a cutting edge of materials synthesis science,” says Wang. “We’re thinking that crystallization is not as straightforward as people believe.”

Observing those intermediates was no easy feat. Enter Wang’s colleague Paul Voyles, a microscopy expert who leveraged UW-Madison’s unique facilities to perform sophisticated scanning transmission electron microscopy measurements, enabling him to detect the tiny structures.

From there, the researchers determined those intermediates lowered the lifetime of titanium dioxide thin films by leading to spikes of electronic current that ate tiny holes in the protective coatings.

Eliminating those intermediates—thus extending the coating‘s lifetime—is as simple as using a thinner film.

Thinner films make it more difficult for intermediates to form within the film, so by reducing the thickness by three quarters (from 10 nanometers to 2.5), the researchers created coatings that lasted more than five times longer than traditional coatings.

And now that they’ve discovered these peculiar structures, the researchers want to learn more about how they form and influence amorphous film properties. That’s knowledge that could reveal other strategies for eliminating them—which not only could improve performance, says Wang, but also open new opportunities in other energy-related systems, such as catalysts, solar cells and batteries.

“These intermediates could be something very important that has been overlooked,” says Wang. “They could be a critical aspect that controls properties of the film.”

 Explore further: Discovery brings renewable fuel production one step closer to reality

More information: Yanhao Yu et al. Metastable Intermediates in Amorphous Titanium Oxide: A Hidden Role Leading to Ultra-Stable Photoanode Protection, Nano Letters (2018). DOI: 10.1021/acs.nanolett.8b02559

Journal reference: Nano Letters  

Provided by: University of Wisconsin-Madison

 

New Center for Sustainable Nanotechnology to study environmental footprint of nanoparticles

Posted: Nov 29th, 2012

(Nanowerk News) Northwestern University has joined  forces with four Midwestern universities and a national laboratory to establish  the Center for Sustainable Nanotechnology, which this fall received  funding from the National Science Foundation.

Chemists, environmental engineers and freshwater scientists will  work on developing a deeper understanding of nanotechnology’s environmental  footprint and potential toxicity — areas little understood, despite a rapid  increase of nanomaterials used in consumer products, from cellphones and laptops  to sunscreen and beer bottles.

“We need to know how the tiny particles interact with their  environment, and this requires advanced imaging and spectroscopic tools that can  see where no eye has seen before,” said Franz M. Geiger, a professor of chemistry in the Weinberg  College of Arts and Sciences who is leading the Northwestern team.

“And the nanoparticles must be studied without taking them out  of their biogeochemical environment or modifying them for analysis,” he said. “This is an extremely daunting challenge but one we relish.”

Geiger’s team includes Stephanie Walter, Julianne Troiano and  Laura Olenick, all doctoral students in his lab. They will utilize their unique  nonlinear optics laboratory to develop new imaging techniques and provide  testing grounds for nanoparticles created by other center members.

Robert Hamers, a professor of chemistry at the University of  Wisconsin-Madison, is director of the Center for Sustainable Nanotechnology.  Other center members are the University of Minnesota, the University of  Wisconsin-Milwaukee, the University of Illinois and Pacific Northwest National  Laboratory.

“Our center — involving the expertise of researchers at six  different institutions — takes ample advantage of synergy, which, by  definition, produces effects that cannot be produced by summing up the  individual parts,” Geiger said.

Center researchers will focus on understanding how the surfaces of new as well as aged or weathered nanoparticles interact at the molecular level with cell membranes and what kind of biochemical pathways are triggered when these interactions occur. The findings ultimately could help inform the development of federal regulations.

In addition to the molecular studies, the researchers will study  two freshwater organisms, a water flea and a bacterium, feeding them  nanoparticles and tracking the particles using methods to be developed in the  center. The biochemical pathways will be studied to determine if the  nanoparticles have any toxic effects on the organisms.

Some of the nanomaterials produce a signal by lighting up when  light of a certain color is shined on them, allowing the particles to be imaged  inside living organisms. Geiger and his team will apply nonlinear optical  approaches to study a subset of these materials: those that can be accessed  using the suite of ultrafast laser systems available in his laboratory.

The Center for Sustainable Nanotechnology received a three-year,  $1.75 million Phase 1 Center for Chemical Innovation grant from the National  Science Foundation (NSF) this fall. Following the initial phase, the researchers  will have the opportunity to apply to the NSF for a much larger grant to  continue their work.

Geiger’s research with the new center connects to Northwestern’s  strategic plan goals of discovering creative solutions to problems that will  improve lives, communities and the world as well as focusing on nanoscience, one  of Northwestern’s 10 areas of greatest strength.

Source: Northwestern  University

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Sunflowers inspire efficient solar power

By Emily Eggleston    |  Sun, 09/30/2012 – 4:21pm

In August, UW-Madison researcher Hongrui Jiang published his design for solar panels that act like sunflowers, tracking the sun’s movement throughout the day. Jiang, a professor in computer and electrical engineering, used nanotechnology to design a system that helps the panels move by reacting to the warmth of the sun’s rays, rather than using a motor and global positioning system (GPS) as many solar tracking panels do. Read Jiang’s answers to Madison Commons’ questions about how the new solar technology works and what else he is doing with nanotechnology.

 

MC: Why are you interested in solar technology?

HJ: Renewable energy is very important right now because we are running out of fossil fuels. We have to look for other possible sources of energy. Solar energy is very promising because pretty much everywhere has sunlight, not like wind or geothermal, and it lasts forever.

MC: Describe the work you do in patterning solar panel movement after sunflowers.

HJ: The basic idea is solar-tracking. If you can have a solar panel follow the sun during the day, you’ll have more interception of light, and therefore more electricity. The idea is very simple and done by many plants in nature. Sunflower is one example, a buttercup flower is another. The idea is very simple but not easy to realizing it with solar plans is complicated because you have to mimic complex biochemical processes.

MC: Don’t some solar panels already track the sun’s movment?

HJ: In the solar tracking systems available now, most use GPS with motors. They are active mechanical systems to orient towards sun. Active systems are great but mechanics consume energy themselves. The purpose is to get as much electricity as possible. Our system is passive, it doesn’t consume electricity to drive solar tracking. Also, it is very hard for active systems to realize full range tracking, sunrise to sunset. Ours does.

MC: How does the passive system of solar tracking work?

HJ: We needed a material that would respond to natural sunlight, whole spectrum light of all wavelengths. has to be sensitive enough. Some materials are responsive to strong light like lasers, but we need the solar panel to be responsive to whatever intensity the sunlight is at. Sunlight hits a mirror which projects light onto actuator holding carbon nanotubes. When the nanotubes warm they contract, causing the panel to shift toward the contracted nanotubes.

MC: You use nanotechnology in your some of your other research. What else do you do on the super tiny nano scale?

HJ: My expertise in the microsystems and microscale optics. I’m working on making a tunable liquid contact lens that adds extra focusing power. When you are getting older the muscle in your eye starts to lose power and it becomes harder and harder for you to see up close so people wear bi- or trifocals. This contact lens autofocuses, basically like the point and shoot cameras that you use. It’s not just a lens, it’s a whole spectrum of gadgets [with] circuits and everything, but it has to be flexible. You need an energy source to provide electricity for the circuits. Right now we’re trying to harvest and store solar energy right in the lens. It’s a very challenging idea and we’re off to a good start.